A scroll compressor possessing low vibration and noise characteristics is arranged in such a manner that a suction chamber is disposed on the outer portion thereof, a discharge port is formed at the central portion of the spiral and the compressed fluid flows in a single direction. Therefore, a discharge valve for compressing the fluid, which has been conventionally provided for a reciprocating type compressors or a rotary type compressors, can be eliminated from the structure, and a constant compression ratio can be realized. Furthermore, the discharge pulsation can be reduced depending upon the operational conditions of the compressor and a necessity of having a large discharge space can be eliminated. Therefore, the development and application of the scroll compressor to a variety of fields in terms of the practical use have been made.
However, since its compression chamber must have a multiplicity of sealing portions, it suffers from an excessively large leakage quantity of the compressed fluid. In particular, it is necessary for a small discharge capacity type scroll compressor for use as a home air conditioning refrigerant compressor to extremely improve the dimensional accuracy of the spiral portion in order to minimize the gap in the compression portion from which the leakage will take place. However, the complicated shapes of the parts and the dimensional deviations of the spiral portion raise the cost of the scroll gas compressor, and uniform performance cannot easily be realized. In particular, the gas leakage cannot be easily prevented when the compressor is being operated at low speed because of the too long compression time. Therefore, there arises a problem that the compression efficiency is unsatisfactory in comparison to that obtainable from the reciprocating type compressors and the rotary type compressor.
In order to overcome the above-described problems, the dimensional accuracy of the spiral portion is made to be at a proper level and the compression efficiency is improved by the oil film seal effect by utilizing lubricating oil in order to prevent the gas leakage which will take place during the compression operation. As disclosed in Japanese Patent Laid-Open No. 57-8386, a proper quantity of lubricating oil is injected into the compression chamber, which is performing the compression operation, so as to seal the gaps of the compression chamber with the film of the lubricating oil so as to overcome the above-described problems.
In particular, the scroll refrigerant compressors have been put into practical use in a refrigerating and air conditioning fields. Therefore, medium to large size compressors such as a package air conditioner and a tiller unit and the like having a relatively large refrigerant capacity per one suction process have been already mass-produced.
FIG. 1 illustrates a structure arranged for the purpose of reducing the fluid leakage from the compressor chamber in such a manner that fluid of an intermediate pressure level introduced from outside the compressor via a fluid path 1130 is urged against the back side of a rotary scroll 1130 so as to push the rotary scroll 1130 toward a fixed scroll 1110. Furthermore, spiral seal members 1117, 1118 (1145, 1180) urged by springs 1170 and 1181 are fastened to a spiral groove 1146 (see FIGS. 2 and 3) formed at the front portions of the spiral wraps 1132 and 1116 of the two scrolls. As a result, the portion between a surface 1133 of an end plate 1131 of the rotary scroll 1130 and the front portion of a wrap 1116 of the fixed scroll 1110 and a portion between a surface 1136 of an end plate 1111 of the fixed scroll 1110 and a front portion 1149 of a lap 1132 of the rotary scroll 1130 are respectively sealed (specification of U.S. Pat. No. 3,994,636).
However, the structure arranged as shown in FIG. 1 in such a manner that the seal members 1117 and 1118 are fastened to the corresponding front portions of the two wraps 1132 and 1116 of the corresponding rotary scroll 1130 and the fixed scroll 1110 so as to axially seal the compression chamber encounters a problem in that the compressor will be damaged by the abnormal pressure rise generated due to the continuous liquid compression taking place in the compression chamber because the seal members 1117 and 1118 disposed at the two end portions prevent the cancellation of the sealing the compression chamber when the rotary scroll 1130 separates from the fixed scroll 1110 in the axial direction due to the generation of the liquid compression, which takes place in the compression chamber, to cancel the sealing of the compression chamber in the axial direction.
Accordingly, an object of a first invention of this application is to quickly leak the compressed fluid through an axial gap of the compression chamber so as to instantaneously lower the pressure when an abnormal pressure rise takes place in the compression chamber.
An object of a second invention is to provide a start load reduction device capable of reducing the start load of the compressor and improving the compression efficiency immediately after the start of the operation.
An object of a third invention is to provide a compressor exhibiting excellent durability of the sliding portion thereof and capable of eliminating vibrations and noise at the initial stage of the start of the operation by reducing the start load of the compressor and by gradually shifting the operation to the full compression mode with the lapse of time after the start of the operation.
In order to achieve the above-described objects, a first invention of a scroll compressor according to the present invention is characterized in that: a rotary scroll is disposed between a body frame supporting a drive shaft and stationarily connected to a fixed scroll and the fixed scroll while allowing a small axial directional movement; a seal member is disposed while allowing a small gap in a spiral groove formed at only the front portion of a spiral wrap of the rotary scroll; the rotary scroll is pushed toward the fixed scroll by the back pressure urging force generated from fluid introduced into a back pressure chamber formed in the rotary scroll in its portion opposing the compression chamber; and the portion between the front portion of a spiral wrap of the fixed scroll and a wrap support disc supporting the wrap of the rotary scroll is sealed.
The second invention is characterized in that: compressed fluid in a compressed chamber in the final compression stroke is introduced into the back side of a thrust bearing which supports a rotary scroll and the thrust bearing is supported by the back pressure urging force.
The third invention is characterized in that: a space present on the back side of a thrust bearing which supports a rotary scroll and a compression chamber at the final compression stroke are allowed to communicate with each other; the thrust bearing is supported by the back pressure urging force of compressed fluid introduced from a compression chamber; and a throttle path is formed at an intermediate position of a communication path.